Generally, a drug is administered into a living body and reaches its affected site, and induces a therapeutic effect by locally exhibiting its pharmacological effect at the affected site; however, even if the drug reaches tissues (that is, normal tissues) other than the affected site, the drug will not contribute to any medical treatment.
Accordingly, what is important is how to efficiently deliver the drug to the affected site. The technique of guiding the drug to the affected site is called drug delivery, and this is a field in which researches and development have been actively conducted in recent years. This drug delivery has at least two advantages. One advantage is that a sufficiently high drug concentration can be obtained in the affected site tissues. Specifically speaking, pharmacological effects will not be obtained unless the drug concentration at the affected site is of a certain level or higher; and the therapeutic effects cannot be expected with a low concentration. However, a sufficiently high drug concentration can be obtained at the affected site tissues by guiding the drug to the affected site.
The second advantage is that side effects to the normal tissues can be suppressed and a drug dosage can be limited to the minimum necessary by guiding the drug to only the affected site tissues.
Such drug delivery is most effective in cancer treatment using anticancer agents. Since most anticancer agents inhibit the cell growth of cancer cells which divide actively, they also inhibit the cell growth of tissues, whose cells divide actively, in normal tissues such as bone marrow, hair roots, digestive tract linings and the like. Thus, a cancer patient to whom an anticancer agent is administered become subject to side effects such as anemia, hair loss, and vomiting.
Since these side effects impose a heavy burden on the patient, it is necessary to limit the dosage. So, the problem is that the pharmacological effects of the anticancer agent cannot be sufficiently obtained. In a worst case scenario, there is a possibility that the side effects may kill the patient.
Thus, it is expected that cancer treatment can be performed effectively while suppressing the side effects by guiding the anticancer agent to the cancel cells by means of drug delivery and making the anticancer agent exhibit the pharmacological effects on the cancer cells in a concentrated matter.
Local anesthetics have similar problems. A local anesthetic is used to treat hemorrhoidal disease, stomatitis, periodontal disease, dental caries, tooth extraction, and local itching or pain of mucous membranes or skin due to surgeries or the like. Lidocaine (product name: Xylocaine) is known as a representative local anesthetic. Although Lidocaine is superior in terms of instantaneous effect, it also has an anti-arrhythmic effect if it spreads systemically; and, therefore, Lidocaine affects a heart significantly.
Moreover, upon performing spinal anesthesia, if Lidocaine is injected as an anesthetic into a spinal fluid, it spreads within the spinal fluid; and there is a possibility that it might cause critical side effects by reaching spinal cords in a cervical region and causing damage to a respiratory function.
As a specific method of the drug delivery, for example, there is a method of using a carrier. This method is to have a carrier which can be easily concentrated at the affected site carry the drug and deliver it to the affected site.
A magnetic substance is considered highly probable as the carrier and there is a proposed method of attaching a carrier, which is a magnetic substance, to the drug and accumulating the drug at the affected site by means of a magnetic field (for example, see Patent Literature 1).
However, it has been found that when the magnetic substance is used as the carrier, oral administration is difficult, carrier molecules are generally enormous, and there are technical problems in binding intensity and affinity between the carrier and drug molecules. So, the practical use of the magnetic substance was difficult in the first place.
Therefore, the inventor of the present invention suggested a metal-salen complex compound as an organic magnetic compound that is anticarcinogenic by itself and is capable of binding with functional molecules such as other medical molecules, enzymes, and proteins (for example, see Patent Literature 2). In this case, the metal-salen complex compound administered to an individual can be guided to a target tissue by a magnetic field applied to the individual. Therefore, it is possible to proceed with a drug treatment, while localizing the effects of the metal-salen complex compound at a target affected site tissue and reducing its side effects.
Moreover, a review article about an organic magnetic substance is introduced, which describes that a magnet is produced with polymeric materials by means of synthesis of “high-spin molecules” having more parallel spins than those of conventional metallic magnetic substances (for example, see Non Patent Literature 1).
Furthermore, a technique that replaces platinum contained in cisplatin with another element is also introduced (for example, see Non Patent Literature 2).